Steam-turbine power plants or just “steam power plants,” for short, are known.
A steam power plant is a type of thermal power plant for generating electricity from fossil fuels, in which thermal energy from steam—in this case—is converted in a steam turbine system or in a steam turbine to energy of motion and is converted further in a generator into electrical energy.
In the case of such a steam power plant, the steam necessary for operating the steam turbine is first generated in a steam boiler, heated by means of the fossil fuel, from (feed) water that has generally previously been cleaned and prepared. By further heating of the steam in a superheater, the temperature and specific volume of the steam increase.
From the steam boiler, the steam flows via pipelines into the steam turbine, where it gives off part of the energy it has previously taken up to the turbine as energy of motion. Coupled to the turbine is a generator, which converts mechanical power into electrical power.
After that, the expanded and cooled steam flows into the condenser, where it condenses by heat transfer to the surroundings and collects as liquid water.
By passing through condensate pumps and preheaters, the water is intermediately stored in a feed-water tank and then fed via a feed pump once again to the steam boiler, thereby completing a cycle (“original power plant process”).
A distinction is drawn between various types of steam power plant—depending on the fuel that is used for generating the steam—such as for example coal-fired power plants or oil-fired power plants.
Other categories of thermal power plants are also known, such as for example gas-turbine power plants (also gas power plants for short) or—as a combination of gas and steam power plants—so-called combined gas-and-steam power plants or gas-and-steam turbine power plants (also combined cycle power plants for short).
A gas power plant is a thermal power plant with a gas turbine system comprising a compressor, a combustion chamber with usually a number of burners, and a gas turbine for generating electricity.
A gas-turbine power plant is operated with fluid fuels. These fuels are generally hydrocarbons, alcohols, coal gas or natural gas. These fluids are the fuel for the gas turbine system, the gas turbine of which drives a generator coupled to it for generating electricity.
In the process, the compressor, which is likewise mechanically coupled to the gas turbine and driven by it, initially sucks in fresh air for the combustion process and compresses it to values that usually lie in the range of 15 bar-20 bar.
The compressed air is fed with the fuel to the combustion chamber. There, the mixture of fresh air and fuel is ignited by means of the burner or burners, in order then to burn there, with combustion gases—substantially carbon dioxide, steam, nitrogen and oxygen—reaching temperatures of up to about 1500° C. and higher.
The hot exhaust gases then flow into the gas turbine, in which they give off part of their thermal energy to the gas turbine by expansion as energy of motion.
The mechanical power is then converted by the generator coupled to the gas turbine into electrical power, which is fed as electric current into an electricity supply system (“original power plant process”).
From the gas turbine outlet, exhaust gases or flue gases (rich in carbon dioxide) are carried away either directly or sometimes also via a heat exchanger.
A combined cycle power plant (CCPP) is a thermal power plant in which the principles or cycles of a gas power plant and a steam power plant are combined. The gas turbine serves in this case—by way of its hot exhaust gases—as a heat source for a downstream waste-heat boiler of the steam power plant, which on the customary principles of the steam power plant in turn acts as a steam generator for the steam turbine.
It is also known that a thermal power plant is “run” by means of a so-called control and protection system—as a component part of a power plant—usually by an operator of a control station. In other words, a control and protection system of a power plant, here a thermal power plant, is usually understood as meaning means and methods that serve for controlling and safeguarding the power plant.
Thus, for example, the control and protection system includes indicating all of the information occurring in a power plant—here a thermal power plant—such as for example measured values, process or status data, in the control station and processing it there in a central control and protection computer—as the central monitoring and control unit of the power plant—on the basis of a central monitoring and control plan. Operating states of individual power plant components are thus indicated, evaluated, monitored and controlled there. The operator can use control elements there to intervene in the operating sequence of the power plant—and thereby run the power plant.
With an increasing proportion of volatile energy, for example from renewable, regenerative energy sources, such as in particular solar or wind energy, generated for example by photovoltaic systems/power plants, solar power plants or wind turbines, as part of an energy mix in an energy distribution network, the conventional, thermal power plants feeding energy into the energy distribution network are increasingly taking on the role of supporting the energy distribution network with control energy and serving as a backup in the form of capacity and control energy for the renewable, volatile energy sources or their corresponding power plants.
As part of this role, the actual energy generation as such in the conventional, thermal power plants can recede into the background to such an extent that after shutting down for a long time they are not required (idle) and cool down, so that when they are started up (again) to be in their operating state, a cold start has to be undertaken (for example after being idle for greater than about 56 hours) instead of a warm start (for example after being idle for about 8 hours to 56 hours).
Because of the type of construction of conventional, thermal power plants, such a cold-starting phase may be between 2 and 8 hours, but under some circumstances even up to 10 hours.
In this (starting-up/cold-starting) phase, however, the thermal power plant cannot supply or market any energy “of its own”, but has to buy in energy, for example because of its own demand for energy during/for preheating.
In addition, thermal power plants are not designed or prepared for rapidly repeated shutting down and starting up again, and cold starting also puts an extreme strain on a power plant, which in the case of a cold start of up to 30 hours can mean a decrease in the overall lifetime of a thermal power plant.
It is accordingly desirable to keep the starting up or such a cold-starting phase as short as possible in the case of a thermal power plant and/or to make it have little strain on systems or power plant components.
Here it is known to shorten the starting up or such a cold-starting phase in the case of a thermal power plant by a specific preheating of power plant components, in particular of a turbine system of a power plant; this allows the thermal power plant or its components to be brought to operating temperature more quickly.
For such preheating of a thermal power plant, in particular its components, specifically its turbine or turbine system, energy may be drawn from the energy distribution network.
By means of this (external) energy it is possible to heat an auxiliary steam generator of the thermal power plant, which generates steam of a high quality. This steam is supplied to the turbine/turbine system of the thermal power plant and flows through the turbine/turbine system, whereby the latter is preheated or heated through.
Once sufficient heating of the turbine/turbine system has been achieved, the turbine/turbine system can be activated and then slowly brought up (to an operating point of the thermal power plant or to full load).
Other components that are to be preheated or can be preheated in the case of a thermal power plant are the (steam) boiler or (steam) boiler casing or shaft.
The time is determined here by the components to be preheated in the thermal power plant that have the thickest walls, for example the shaft and the high-pressure steam casing in the case of a steam power plant or the steam turbine system there, since these power plant components need the longest to heat through.
Thus, for example, a modern combined cycle power plant requires about 4 hours for a cold start.
Also known—for shortening cold-starting phases or starting-up times in the case of thermal power plants, here combined cycle power plants—are so-called “Advanced FaCy” or “Hot on the fly” (a “flying start”) (“Improvement of operational efficiency based on fast startup plant concepts”, Ulrich Grumann et al., Siemens AG Energy Solutions, XXIst World Energy Congress, Montreal, Sep. 12-16, 2010).
In the case of “Advanced FaCy” or a “flying start”, the steam turbine of the combined cycle power plant is started up approximately parallel with the gas turbine heating the steam turbine with waste heat, whereby hot steam is admitted to the steam turbine immediately and extremely, but still below its load limit or maximum requisite heating temperature gradient—and consequently it is quickly “brought to temperature”. Start-up times in the case of combined cycle power plants can be significantly reduced in this way.
A disadvantage of “Advanced FaCy” or a “flying start” is that its implementation in existing thermal power plants requires a corresponding, complex (subsequent) installation (of power plant hardware and software).
Another disadvantage of “Advanced FaCy” or a “flying start” is that primary energy has to be used for this—with additional costs thus arising. In other words, for example, gas is burned in the gas turbine, and with it the steam part is heated.
Other approaches to countering the cold starting problems described that affect thermal power plants are that of keeping power plant components (permanently) hot, operating the thermal power plant continuously at full load or reducing the power plant to just partial load. However, these approaches entail economic, ecological and/or technical disadvantages and risks.
A classification of energy storage devices, with corresponding examples and properties of such energy storage devices, is known.
Accordingly, energy storage devices can be classified as thermal energy storage devices (heat storage devices, district heat storage devices, thermochemical heat storage devices, latent heat storage devices), chemical energy storage devices (inorganic: galvanic cell (rechargeable battery, battery), redox-flow cell, hydrogen, battery storage power plant; organic: ADP, ATP, AMP, glycogen, carbohydrates, fats, chemical hydrogen storage device), mechanical energy storage devices (kinetic energy (energy of motion): flywheel or flywheel storage device; potential energy (positional energy): spring, pumped storage power plant, compressed air storage power plant, gravity storage power plant) and electrical energy storage devices (capacitor, superconductive magnetic energy storage device).
EP 2 351 912 A1 discloses a thermal power plant with a heat storage device that is designed to supply (thermal) energy for heating a turbine of the thermal power plant when starting up the thermal power plant.
DE 10 2010 041 144 A1 describes a thermal power plant with a pressure storage device. This pressure storage device—with fluid under pressure there—is designed to supply energy when starting up the thermal power plant—in the form of or by feeding the compressed fluid from the pressure storage device into a machine that generates rotational energy for a turbine of the thermal power plant, and thus drives it—for the operation of the turbine during its starting/starting up.
DE 41 38 288 A1 discloses a thermal power plant with an electrical energy storage device which is designed to supply electrical energy into an energy distribution network during the operation of the power plant to compensate for brief peaks in load.